The physical arrangement of the components of an in-line turboprop engine for small business aircraft generally includes in succession beginning from the forward end of the engine, a propeller, an engine exhaust, the engine core, the engine's air intake, a tank for storing lubricating oil, an accessory gearbox and auxiliary accessories that are powered via the accessory gearbox. Thus, the engine core is disposed aft of the engine exhaust, and the air intake is disposed aft of the engine core.
The flow of gasses through the gas turbine engine proceeds from the engine's air intake and proceeds generally downstream toward the engine's exhaust. The gas turbine engine generally includes, in serial fluid flow order, the air intake, a compressor section, a combustion section, a high pressure turbine section, a power turbine section and an exhaust section. Air is drawn into the air intake and compressed by the compressor in the compressor section. Fuel is added to the compressed air in the combustion section, and the fuel-air mixture is combusted in the combustion section to produce hot combustion gases that expand successively through the high pressure turbine section and then the power turbine section and produce rotational mechanical energy that can be tapped to drive one or more shafts that are coupled to the high pressure turbine and the power turbine.
A number of auxiliary accessories are mounted to the aft end of the engine and may include such accessories like a starter, a fuel pump, and an electric generator. The power to drive these auxiliary accessories is taken off the rotation of the compressor shaft via an accessory gearbox that receives its lubrication from an accessory oil tank that is disposed between the engine's air intake and the accessory gearbox. The accessory oil tank also typically is sized to house the pump that transfers the oil from the oil tank to the accessory gearbox and to other lubrication sites within the engine. The forward end of a quill shaft is splined into the aft end of the compressor shaft, and the quill shaft extends axially through the accessory oil tank and into the accessory gearbox. The aft end of the quill shaft has a pinion gear that meshes with a power takeoff gear that is rotatably mounted within the accessory gearbox to distribute rotatable power that drives the accessory driveshafts that in turn power the auxiliary accessories that are mounted to the aft end of the accessory gearbox. The quill shaft is rotatably supported by at least two bearings, and there are seals where the quill shaft extends through each of the forward and aft walls of the accessory oil tank, which has an interior that defines an annular space in which the lubricating oil is stored. The propeller, the power turbine shaft, the compressor shaft and the quill shaft all rotate about the same axis of rotation and are arranged successively in line end-to-end with each other.